The invention relates to a circuit configuration for matching an output impedance of an amplifier to a radio-frequency line, and to use of the circuit configuration. The circuit configuration is used for matching single-way power amplifiers for dual-band mobile telephones. In one-way power amplifiers, the matching to the 900 MHz (GSM, D1, D2 network) or 1800 MHz band is carried out by switching the matching circuit.
In the past, an external negative voltage source was disadvantageously required in addition to a positive voltage source for switching the matching circuit in one-way power amplifiers.
Dual-band radio telephones with two-way amplifiers are costly, due to the necessity to duplicate the configuration of the transmission paths as far as the antenna.
Various circuit variants for a signal input circuit using a PIN diode are disclosed in German Patent DE 32 10 453 C2. The PIN diode is in each case connected to the signal input via reactive elements. The other connection of the diode may be connected via a capacitor to ground. The signal is passed via an inductance to an amplifier element, which is in the form of a transistor.
It is accordingly an object of the invention to provide a circuit configuration for matching an amplifier to a radio-frequency line that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which not only has just one transmission path for two different frequency bands, but also does not require any external negative voltage source.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for matching an amplifier to a radio-frequency line. The circuit configuration contains a first diode having a first terminal and a second terminal to be connected to a first potential, an inductor having a first terminal and a second terminal, and a first capacitance having a first terminal connected to the radio-frequency line and a second terminal connected to the first terminal of the first diode and to the first terminal of the inductance. A second diode is provided and has a first terminal coupled to the first capacitance and a second terminal. A first resistor is provided and has a first terminal connected to the second terminal of the inductance and a second terminal. A second resistor has a first terminal connected to the second terminal of the first resistor and a second terminal. A switching device has a first terminal connected to the second terminal of the first resistor and to the first terminal of the second resistor. The switching device has a second terminal to be connected to a second potential. A second capacitance has a first terminal connected to the second terminal of the second resistor and to the second terminal of the second diode. The second capacitance has a second terminal to be connected to the first potential.
Thus, for example, it is advantageous to connect a third resistor between the second diode and the inductance. This makes it possible to limit the current flowing through the second diode.
In accordance with an added feature of the invention, the first diode is a PIN diode, the second diode is a Schottky diode, and the switching device is an audio frequency transistor.
The circuit configuration is ideally used in combination with a dual-band radio (mobile) telephone having a transmission path which can be used for different frequency bands. The circuit configuration matches an amplifier to the different frequency bands.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration for matching an amplifier to a radio-frequency line, and use of the circuit configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.